The role of carbonic anhydrase in photosynthesis and the activity of the carbon‐concentrating‐mechanism in bryophytes of the class Anthocerotae

Abstract

The role of carbonic anhydrase in the carbon-concentrating-mechanism of bryophytes of the class Anthocerotae was investigated by comparing the gas-exchange characteristics of material which had been incubated in the membrane-permeable Carbonic Anhydrase inhibitor ethoxyzolamide, with those of untreated material and material which had been incubated in buffer solution. In Phaeoceros laevis (Anthocerotae), incubation in ethoxyzolamide caused a depression in the rate of gross assimilation and a decrease in CO # affinity beyond that which could be attributed to increased diffusion limitation. A range of liverworts and mosses, in which a carbonconcentrating-mechanism is absent, were also investigated. These showed no depression of rates of gross assimilation after incubation in ethoxyzolamide relative to those of untreated material. The CO # compensation point and CO # uptake characteristics of Phaeoceros laevis were significantly affected by incubation in ethoxyzolamide. Values of CO # compensation point for Phaeoceros laevis rose from 2.5 Pa, after incubation in buffer, to 20 Pa after incubation in ethoxyzolamide. The CO # compensation point for the liverworts Pellia epiphylla and Marchantia polymorpha was not significantly affected by incubation in ethoxyzolamide. Measurements of the release of CO # at the end of a short (15 min) period of illumination revealed that, after suppression of carbonic anhydrase activity, the rapid release of a CO # pool occurred in Phaeoceros laevis but not in the liverworts. There were also significant differences between values for fractionation measured in units per mil (=), measured instantaneously, for Phaeoceros laevis incubated in ethoxyzolamide, compared with fractionation values for this species after incubation in buffer. Incubation in ethoxyzolamide caused fractionation values to rise from 12.4-22.7=, indicating that the carbon-concentrating-mechanism of this species had been inactivated. Incubation in ethoxyzolamide had no effect on fractionation values for the liverworts. The convexity of the light saturation curves of liverworts and Phaeoceros laevis was also investigated, but there were no differences between groups before or after the two treatments. The data indicate an important role for carbonic anhydrase in the functioning of the carbon-concentrating-mechanism in the Anthocerotae.

Fossil bryophytes as recorders of ancient CO2 levels: Experimental evidence and a Cretaceous case study

“…, close to but lower than a published estimate of $2.0 mmol m À2 s À1 at ambient CO 2 [Smith and Griffiths, 2000;Hanson et al, 2002;Griffiths et al, 2004]. The lower calculated value may reflect the short-term nature of the direct photosynthesis measurements made under optimal conditions, or a lower value of r [Proctor, 1981].…”

“…Photosynthetic CO 2 uptake and D 13 C by bryophytes occur by passive diffusion of CO 2 into the cells and depend on the kinetics of the primary carboxylating enzyme ribulose-1,5-carboxylase/oxygenase (Rubisco), both of which respond to the concentration of atmospheric CO 2 . The only exception is some hornwort species which possess CCMs [Smith and Griffiths, 2000]. Because of their comparatively simple structure, bryophyte D…”

“…In mosses, experimental observations indicate A increases almost linearly with [CO 2 ] a up to around 800 ppm [Silvola, 1985;Williams and Flanagan, 1998]; in liverworts A increases linearly up to around 400 ppm in some but not all species [Smith and Griffiths, 2000;Griffiths et al, 2004] (Figure 1, top). This partly reflects changes in the d 13 C of the assimilated CO 2 , which also became more negative with the addition of increasing amounts of fossil fuel-derived CO 2 (Figure 1, middle).…”

Hornwort pyrenoids, carbon-concentrating structures, evolved and were lost at least five times during the last 100 million years

“…Organic isotope discrimination supports a function in CO 2 concentration for hornwort pyrenoids (14)(15)(16)(17)(18). Mass spectrometry analyses show that hornworts with pyrenoids (e.g., Phaeoceros and Notothylas) have lower compensation points (11-13 vs. 64 ppm) and larger pools of DiC (suggesting an accumulation of inorganic CO 2 ) than the C 3 liverworts, the organisms chosen as the reference point, a comparison across a vast phylogenetic distance.…”

Cloning of SjCA gene and its expression analysis on upland cottons

“…Besides, many salt-tolerant genes were cloned. Carbonic anhydrase (CA, EC 4.2.1.1) containing a zinc atom was cloned and identified to catalyze the reversible conversion between carbon dioxide and bicarbonate radical (CO 2 + H 2 O↔HCO 3¯ ) [6,7] , which plays an important role in many biological processes, such as ion exchange, respiration, pH stabilization, calcification, CO 2 capture, and photosynthesis [8][9][10] . Since 1933, when the CA gene was found in red blood cells, it has also been discovered in all types of mammalian histiocytes.…”